To set up your course, enter edit mode for your course, and select Add an activity or resource. Select External tool* in the resulting dialog box. On the configuration page that results, enter "Perusall" (or anything else) for the activity name and select Perusall from the Preconfigured tool dropdown. Click Save and display to launch Perusall and create your Moodle-linked Perusall course.
If you do not see External tool under Add an activity or resource, choose Perusall 1.3 > Select content, and (under Home Page) click Link to home page.